The present disclosure relates to a transverse electric field type liquid crystal display panel, and in particular, to an FFS (Fringe Field Switching) mode liquid crystal display panel in which a shield electrode is formed on a color filter substrate to face a liquid crystal layer, and which has good transmittance and a drive voltage not so high.
A liquid crystal display panel is lightweight and thin and has low power consumption compared to a CRT (Cathode-Ray Tube), and is thus widely used in many electronic apparatuses for display. The liquid crystal display panel is configured such that the orientation of liquid crystal molecules arranged in a predetermined direction is changed by an electric field, thus the transmitted amount of light of a liquid crystal layer is changed to display an image. A liquid crystal display panel includes a reflective liquid crystal display panel in which external light is input to the liquid crystal layer, is reflected by a reflecting plate, transmits again the liquid crystal layer, and is emitted, a transmissive liquid crystal display panel in which incident light from a backlight device transmits the liquid crystal layer, and a transflective liquid crystal display panel having both the reflective and transmissive portions.
As a method of applying an electric field to the liquid crystal layer of the liquid crystal display panel, there are a longitudinal electric field type and a transverse electric field type. A longitudinal electric field type liquid crystal display panel is configured such that an electric field in a substantially longitudinal direction is applied to liquid crystal molecules by a pair of electrodes arranged with a liquid crystal layer sandwiched therebetween. As the longitudinal electric field liquid crystal display panel, there are a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, an MVA (Multi-domain Vertical Alignment) mode, and the like. A transverse electric field type liquid crystal display panel is configured such that a pair of electrodes are provided on the inner surface of one of a pair of substrates arranged with a liquid crystal layer sandwiched therebetween to be insulated from each other, and an electric field in a substantially transverse direction is applied to liquid crystal molecules. As the transverse electric field type liquid crystal display panel, there are an IPS (In-Plane Switching) mode where a pair of electrodes do not overlap each other in plan view, an FFS mode where a pair of electrodes overlap each other in plan view, and the like.
Of these, an IPS mode liquid crystal display panel is configured such that a pair of electrodes including a pixel electrode and a common electrode are comb-shaped to be meshed with each other in a state of being electrically insulated from each other, and an electric field in a transverse direction is applied to liquid crystal between the pixel electrode and the common electrode. The IPS mode liquid crystal display panel advantageously has a wide viewing angle compared to the longitudinal electric field type liquid crystal display panel.
An FFS mode liquid crystal display panel is configured such that a pair of electrodes including a common electrode and a pixel electrode are arranged in different layers through an insulating film, a slit-shaped opening is provided in the common electrode or the pixel electrode facing the liquid crystal layer, and an electric field in a substantially transverse direction which passes through the slit-shaped opening is applied to a liquid crystal layer. The FFS mode liquid crystal display panel can obtain a wide viewing angle and improve image contrast, and is increasingly used in recent years. As the FFS mode liquid crystal display panel, there are a liquid crystal display panel where the common electrode and the pixel electrode are formed on the substantially same plane as a thin film transistor (TFT) serving as a switching element, and a liquid crystal display panel where the common electrode and the pixel electrode are both arranged above the TFT.
Of these, in the FFS mode liquid crystal display panel where the common electrode and the pixel electrode are both arranged above the TFT, the surface of the TFT or the like is coated with an interlayer resin film, and a lower electrode formed of a transparent conductive material and an upper electrode having a slit-shaped opening are formed on the surface of the interlayer resin film with an inter-electrode insulating film sandwiched therebetween. The upper electrode and the lower electrode can be both operated as the pixel electrode and the common electrode.
While in the longitudinal electric field type liquid crystal display panel, the common electrode is formed on the transparent substrate to face the display surface, in the transverse electric field type liquid crystal display panel, no electrode is formed. For this reason, in the transverse electric field type liquid crystal display panel, the alignment of liquid crystal molecules may be disturbed due to static electricity from the outside, such as a person's finger. Thus, as the transverse electric field type liquid crystal display panel, JP-A-2008-209529 describes a liquid crystal display panel in which a transparent conductive electrode (hereinafter, referred to as “shield electrode”) for static electricity prevention is molded on the transparent substrate of the color filter substrate to face the display surface so as to prevent an image from being disturbed due to static electricity.
Further, as the transverse electric field type liquid crystal display panel, JP-A-2008-129405 describes a liquid crystal display panel in which a shield electrode is molded on the transparent substrate of the color filter substrate to face the liquid crystal layer. Hereinafter, the shield electrode which is molded on the transparent substrate to face the display surface is referred to as “outside shield”, and the shield electrode which is molded on the transparent surface to face the liquid crystal layer is referred to as “inside shield”.
In the case of an outside shield, the upper electrode or lower electrode which is operated as the pixel electrode and the shield electrode are away from each other by equal to or greater than the thickness of the transparent substrate. Thus, even when a longitudinal electric field formed between the shield electrode and the pixel electrode is applied to the liquid crystal layer, advantageously, there is little influence on transmittance. Therefore, in the case of the outside shield, transmittance is high, and there is little variation between the directions of the electric field in the subpixels, and as a result, the drive voltage can be reduced.
In contrast, in the case of an inside shield, it is advantageous in that the shield electrode can be formed on the transparent substrate to face the liquid crystal layer by the same step as the forming step of the common electrode in the longitudinal electric field type liquid crystal display panel of the related art. Therefore, in the case of the inside shield, even when a liquid crystal display panel for a large plate is used, it is not necessary to newly provide a large-scale device for inside shield electrode formation. Further, in the case of the inside shield, since the shield electrode is not exposed to the outside, the shield electrode is unlikely to be damaged. In particular, it is effective for a liquid crystal display panel on which a finger touches. As described above, the outside shield and the inside shield respectively have advantages and disadvantages, thus both are appropriately selected and manufactured.